Image: NASA/ESA HUBBLE SPACE TELESCOPE |
Astronomers have discovered a small, faint object about 13.4 billion light years away that they suspect represents one of the building blocks of present-day galaxies. The new finding, to be described in the Astrophysical Journal Letters, may thus shed light on how and when the first stars and galaxies formed.
Richard Ellis of the California Institute of Technology and colleagues made the observations using the Hubble Space Telescope and the Keck Telescopes. These instruments are not powerful enough to detect such objects on their own. Fortunately, they had the benefit of a natural magnifier, a phenomenon known as gravitational lensing. Clusters of galaxies between the telescopes and their far-off quarry magnify the light coming from those distant objects, functioning as cosmic lenses. In this case, the Abell 2218 galaxy cluster (see image) magnified a far-off infant galaxy¿s weak light more than 30 times. Even so, "it took two observing runs with the Keck Telescope before we had gathered enough light from this feeble object to determine its distance and thus confirm the discovery," team member Jean-Paul Kneib from the Observatoire Midi-Pyrenees, France, recalls. "When we realized what we had found, we literally jumped up and down."
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Some 500 light-years in diameter (as compared with our 100,000 light-years across Milky Way), the newly discovered galaxy (inset) contains 100,000 times less matter than our own and is a mere two million years old. "We believe it is one of the galaxy building blocks that join together and make up larger galaxies later in the history of the Universe," Konrad Kuijken of the Kapteyn Institute in the Netherlands remarks. "With this discovery, we may finally be witnessing the circumstances in which this first generation of stars was born."